To ensure cell survival and maintain genomic integrity, chromosomes must be equally distributed to daughter cells during mitosis. The kinetochore is a specialized region of the chromosome that binds microtubules of the mitotic spindle. All eukaryotes use kinetochores to segregate chromosomes during mitosis but how the kinetochore is established and maintained on each eukaryotic chromosome is unknown. The chromatin of the kinetochore is unique in that histone H3 is replaced with the histone variant centromere protein A (Cenp-A). The incorporation of Cenp-A into chromatin identifies the chromosomal position of the kinetochore and is essential for kinetochore assembly. This proposal is focused on understanding how cells specify the position of the kinetochore and how kinetochores are assembled at that site. We propose genetic, biochemical and cell biological methods to understand how Cenp-A is specifically incorporated into chromatin. We will first identify and characterize factors that are important for establishing and maintaining Cenp-A at kinetochores. Our first specific aim is to identify genes that are important for Cenp-A localization by RNAi based screening of the Drosophila genome. Using affinity biochemistry we have isolated a chromatin-remodeling enzyme that binds specifically to Cenp-A. Our second specific aim is to characterize the function of this enzyme in centromeric chromatin formation. Our third specific aim is to use the cell free Xenopus egg extract system as an in vitro system to dissect the mechanisms of kinetochore assembly. By combining the discovery of proteins that regulate kinetochore assembly with in vitro systems and cellular assays to analyze their functions we hope to understand how kinetochores are specified and assembled. [unreadable] [unreadable]